This invention relates to a catalyst regeneration procedure. More particularly, this invention relates to a catalyst regeneration procedure wherein the catalyst is a hydrogenation catalyst. Specifically, the invention provides for a catalyst regeneration procedure, use of which provides an increased catalyst life and an improved reaction rate in the hydrogenation of organic compounds possessing at least one carbon-to-carbon bond unsaturation in the presence of a rhodium or ruthenium catalyst and a methylene dichloride solvent.
The Prior Art
The six metals in the platinum metals group -- ruthenium, rhodium, palladium, osmium, iridium, and platinum -- are all hydrogenation catalysts. Palladium and platinum catalysts have been widely used as hydrogenation catalysts for decades. Rhodium and ruthenium catalysts also make excellent hydrogenation catalysts, but their development and usage are not as yet so widely appreciated. Iridium and osmium catalysts, on the other hand, are used as catalysts the least of any of the six platinum metals.
One specific usage of rhodium or ruthenium catalysts is in the hydrogenation of unsaturated epoxy compounds as taught in Shokal, U.S. Pat. No. 3,336,241. In Shokal, aliphatic or cycloaliphatic epoxy ethers are prepared by treating compounds possessing carbon-to-carbon unsaturation and at least one vic-epoxy group with hydrogen in the presence of a finely-divided catalyst containing a metal of an atomic number from 44 to 45 inclusive, i.e., a metal of the group consisting of rhodium and ruthenium, preferably supported on an inert carrier such as charcoal or alpha-alumina at a temperature below about 150.degree.C. In the hydrogenation step, the unsaturation linkages are selectively hydrogenated, leaving the epoxy groups substantially intact.
Rhodium or ruthenium catalysts are relatively expensive, and accordingly, it is essential to be able to hydrogenate a large quantity of organic compounds per unit of catalyst. Product yields with the typical Shokal process catalyst, for instance, appear to be limited to less than about 15,000 grams of resin per gram of rhodium or ruthenium metal. As with most catalyst systems, rhodium and ruthenium catalysts gradually lose activity and eventually it becomes necessary to either regenerate the catalyst or else reclaim the metal portion of the catalyst. Reclamation of the rhodium or ruthenium metal from the catalyst is expensive and is not an economically viable alternative. Therefore, it is necessary to employ some type of regeneration procedure.
The typical regeneration procedure for a catalyst containing a metal of the platinum metals group involves an oxidation followed by a reduction of the metal. See Rylander, Catalytic Hydrogenation over Platinum Metals, pp 13-15 (1967). Catalytic regeneration through oxidation involves the conversion of strongly adsorbed inactivating materials to compounds more easily removed, as with the oxidation of divalent sulfur, or the actual burning off of carbonaceous deposits found on the catalyst surface. Once the oxidation step of the regeneration procedure has been completed, it is then necessary to reduce the metal oxides thus formed during the oxidation step. This reduction is accomplished by contacting the oxidized catalyst with hydrogen at an elevated temperature. While the above regeneration procedure has been used successively for the regeneration of platinum metal catalysts, including rhodium and ruthenium catalysts, such a procedure cannot be used for the rhodium or ruthenium catalysts employed with methylene dichloride as the hydrogenation solvent. When conventional regeneration techniques are employed, i.e., when the spent catalyst is dried in nitrogen, then oxidized, and then reduced in hydrogen, the catalyst obtained is totally inactive. Without wishing to be bound by any particular theory, it is considered likely that the reason for this inactivity is the destruction of the catalyst active sites by chlorine gas and oxychlorine compounds formed during the oxidation step. It is believed that the chlorine gas and oxychlorine compounds are produced during the oxidation step of the regeneration due to the presence of chlorine compounds on the catalyst surface from the partial breakdown of the methylene dichloride solvent during the hydrogenation reaction.
A catalyst regeneration procedure has now been found that not only increases the life of the catalyst, but also increases the reaction rate associated with the catalyst.